There is an increasing need to provide very cold liquids and very cold gases, generally referred to as cryogens, for industrial and scientific applications. Typically, a cryogen is supplied to a cryostat or other cooling device where it is used as a heat sink to extract thermal energy from a sample in order to cool the sample to a very low temperature. The need to provide cryogens has developed because of the growing interest in desirable properties that are observed in some substances when they are cooled to very low temperatures. One such property is super conductivity, which is a substance's ability to conduct electrical current with minimal internal resistance. To date, super conductivity has been observed in some substances only when they are cooled to very low temperatures.
Currently, most cryogen supply systems are designed to provide cryogen in either a liquid state or a gaseous state. Cryogen supply systems for liquefied state cryogens typically are dewars or other insulated containers that are used to store the cold liquid prior to its delivery to an end use device. These supply systems usually rely on some type of mechanical mechanism to pump the liquid through a supply line to the end use device.
Cryogen supply systems for gaseous state cryogens usually include a sealed dewar or other container for holding liquid state cryogen that has a heating element located in the cryogen containment space. Cryogenic gas is generated by boiling the liquid state cryogen to produce the gas. The gas pressure that develops inside the container as a consequence of the generation of the gas is sufficient to force the gas through a supply line to the end use device.
There are a number of limitations and disadvantages associated with the currently available cryogen supply systems. The mechanical pumps used with liquid state cryogen supply systems are complicated to operate, expensive and can be noisy. Gas state cryogen supply systems must be refilled with liquid state cryogen when they inevitably run dry. The time spent refilling the cryogen supply system with the supercooled liquid interrupts the time the system can be used to supply cryogenic gas. In other words, current gas state cryogenic gas systems cannot readily be used to provide an uninterrupted supply of cryogen for extended periods of time.
Another disadvantage of available gas state cryogen supply systems is the need to have a readily available supply of liquid state cryogen on hand when gas state cryogen supply systems are being used to supply large amounts of cryogen and/or being used to supply cryogen for extended periods of time. In some situations it is difficult to provide sufficient storage place for the needed cryogenic liquid. Moreover, there may be significant costs associated with storing the liquid.
Many current cryogen supply systems are not able to provide cryogenic fluid that, while cold, is at a temperature above that at which it is stored in the supply system. Liquid state cryogen supply systems usually cannot be used to provide cryogenic liquid at temperatures above that at which it is stored in the system. Gaseous state cryogen supply systems may be useful in providing a super cooled gas that is just above its condensation temperature, but cannot be readily used for providing a gas, though cold, is at a significantly higher temperature than the temperature at which it evaporates. This limitation makes it difficult to provide cryogens at selected temperatures above the temperatures of the cryogens stored in the supply system.
Furthermore, there is often a need to supply gaseous state and liquid state cryogen to the same cooling device. This need arises, for example, when it is desirable to cool a sample to a number of different temperatures in order to observe the changes that may occur as its temperature changes. In these situations it is desirable to provide a cooling device with a super cooled liquid at one temperature, and then immediately thereafter with a super cooled gas, that is typically at a temperature above that of super cooled liquid. To date, it has proved difficult to provide a cryogen supply system that can simply and quickly be used to both cryogenic liquid and cryogenic gas.